Without wishing to sound overly critical, you evidently don't understand the economics involved.

Let me give you one definitive price point. I was told some years ago (which means that with inflation the number is probably larger now) that QF were charging other oneworld airlines US$250 per passenger for access to their F lounge in Sydney. My source is impeccable (the CFO of a oneworld airline, who happens to be a friend of mine). I cannot help but think that this is VERY financially worthwhile for QF.

One of the reasons many airlines are spending such huge amounts of money on upgrading their lounges is that they are, in fact, major money spinners - not just a bonus for their own elite passengers and frequent flyers, but revenue (and profit) generators. After all, if this were NOT the case - in other words if taking in passengers from other airlines was revenue-neutral or loss-making - this would seem to indicate that there would be little benefit in airlines opening or upgrading lounges in outstations where alliance partners already had lounges, as they could simply pay cost prices to the incumbent lounge operator. Yet in the last few years, to give another example, each of AA, CX and QF has spent significant sums in upgrading or (in the case of QF) opening lounges in LHR T3. Undoubtedly part of this is for prestige, part of it is a marketing tool to attract customers to their own airline, but a significant part is also to (a) avoid having to pay huge sums to other airlines when passengers prefer their lounges and/or (b) to have the opportunity to charge other airlines access fees if their passengers choose to use that lounge in preference to the one provided by (or contracted by) their own airline.